1. Field Of The Invention
This invention deals with controlling the priority of responses (as opposed to the priority of requests) from a hierarchical store when simultaneous responses are to be handled on a common bus transfer path.
2. Description Of The Prior Art
The prior art on storage priority controls has been noted to use (1) a predetermined priority relationship among simultaneous requests (i.e. demands), and (2) to use different conditions to control priority among simultaneous demands (requests). This invention does not use either (1) or (2) but uses simultaneous responses from hierarchy levels to grant priority among the responses. Examples of prior art are as follows:
U.S. Pat. No. 3,353,160 to A. B. Lindquist provides a system in which priority is controlled by the request position in a tree queue arrangement.
U.S. Pat. No. 3,543,242 to R. L. Adams provided for establishment of priority based on a predetermined priority order among simultaneous input requests. Priority is based on an assigned priority list and the time of each arrival of requests. Higher priority is given when overrun is anticipated.
U.S. Pat. No. 3,478,321 to J. C. Copper et al. discloses a priority system in which request priority is lowered by the busy condition of either a requesting unit or a requested store unit.
U.S. Pat. No. 3,208,048 to Kilburn et al establishes a predetermined request priority based on interrupt requests to different speed devices. A fixed request priority is given according to level. Concurrent transfers to main store 10 from first level substore 54 (drum) and second level substore (55) tape are interleaved by alternating transfer control program.